Cellular communication, which enables the reuse of limited spectrum resources, leads to the flourishing development of wireless communication technologies. In a cellular system, when a service needs to be transmitted between two UEs, service data to be transmitted from a User Equipment 1 (UE1) to a User Equipment 2 (UE2) is first transmitted to a base station 1 via an air interface, then the base station 1 transmits the user data to a base station 2 via a core network, and the base station 2 transmits the service data to the UE2 via an air interface. The data transmission from the UE2 to the UE1 is realized through a similar processing flow. FIG. 1 is a schematic diagram illustrating a cellular system in which UEs are located in the cell(s) of the same base station according to the conventional art. As shown in FIG. 1, when the UE1 and the UE2 are located in the cellular cell of the same base station, although base stations 1 and 2 are actually the same base station, two parts of wireless spectrum resources are consumed in a single data transmission process, and the transmitted data still needs to be forwarded by the core network.
It can be known from above that the foregoing cellular communication scheme is obviously not the optimal one when UE1 and UE2 are located in the same cell and are proximate. Actually, as mobile communication services become increasingly diversified, for example, as social networks and electronic payment are being used more and more widely in wireless communication systems, the demand for service transmission between users located at a near distance from each other increases continuously. Thus, device-to-device communication is drawing more and more attention. The so-called Device to Device (D2D for short) communication refers to the direct transmission of service data from a source UE to a destination UE via an air interface without being forwarded by a base station. FIG. 2 is a schematic diagram illustrating D2D communication according to the conventional art. As shown in FIG. 2, the D2D communication mode is different from the traditional cellular communication mode. For users communicating with each other at a near distance, D2D communication not only saves wireless spectrum resources but also reduces the data transmission workload of a core network.
In cellular communication, one of the references for scheduling is channel state. That is, a Reference Signal (RS for short, also referred to as pilot) is transmitted between a transmitter and a receiver, channel state information (CSI) indicating the state of a channel between a network node and a UE is obtained according to the measurement of the RS and used as a reference for scheduling.
The introduction of the D2D communication in a cellular system also affects the scheduling of service transmission. That is, when UEs are scheduled to perform D2D communication, the scheduling needs to be performed based on the channel state information indicating the state of a channel between the UEs, and this channel state information is obtained by measuring an RS. No solution has been provided in the conventional art to address the problem of the configuration and the transmission of a reference signal in a case where D2D communication is introduced into a cellular system.